The present invention relates to methods and apparatus for dispensing fluid in pre-selected quantities or xe2x80x9cdosesxe2x80x9d, and deals more particularly with a method and apparatus for dispensing fluid doses employing multiple pumps to provide back up pumping capability in the event of a pump malfunction.
Various types of industrial systems often employ apparatus for dispensing pre-selected, discrete amounts or xe2x80x9cdosesxe2x80x9d of a fluid medium for any of various purposes. For example, in connection with semiconductor manufacturing operations for producing semiconductor wafers, wet etching equipment produces waste-water, the pH value of which must be controlled. This is usually accomplished by measuring the pH of the waste-water, and adding doses of an alkaline liquid to the waste-water, from time to time so that the pH level of the waste-water is maintained above some pre-selected, minimum level.
In the past, the alkaline liquid was maintained in a separate tank, and a single pump was used to pump the alkaline liquid from a container thereof into the waste-water tank. In the event that the pump malfunctioned for some reason, and stopped pumping, an audible or visual alarm was issued, thereby alerting the operator that a fault or malfunction had occurred somewhere in the dosing system. Once the operator finally identified the pump as being the component in the system that was out of order, he would manually switch to another pump in order to resume the dosing operation, however the operator did not know at the time of the current malfunction, how much of the alkaline liquid, as a part of the total dose, had been dispensed. Furthermore, in some cases the entire semiconductor line had to be shut down in order to specifically isolate and correct the pump problem, thus reducing processing throughput. In addition to these shortcomings, the prior art process for troubleshooting and correcting pump malfunctions was subject to operator error.
Accordingly, there is a clear need in the art for an improved method and apparatus for dispensing fluid doses which overcomes each of the deficiencies discussed above. The present invention is directed towards satisfying this need.
According to one aspect of the invention, apparatus is provided for dispensing doses of a fluid including first and second pumps coupled with a source of the fluid to be dispensed. Each of the pumps has a fluid output for delivering fluid to a destination, such as a tank of a second fluid. First and second sensing means are respectively provided on the pump outputs to sense when the associated pump is pumping fluid, and is thus operating properly. When either of the pumps malfunctions, and fails to output fluid, the sensing means produces a fault signal which is delivered to electrical control means which responds to either of the fault signals by activating the other pump, thereby providing automatic switching of the two pumps so as to prevent interruption of fluid delivery, and assuring that a full fluid dose is dispensed. The sensing means preferably comprises a fluid switch, such as a butterfly valve acting on an electrical switch. The electrical control means preferably comprises a programmable logic controller, including timing means for timing the duration of fluid delivery from either of the two pumps.
According to another aspect of the invention, apparatus is provided for dispensing doses of a first fluid into a container of a second fluid, comprising first and second fluid pumps coupled with a source of the first fluid for pumping a dose of the first fluid from the source to the container, such time duration being related to the dose of the first fluid being delivered to the container. The apparatus also includes means for sensing when either of the pumps malfunctions, and produces an electrical signal which is delivered to a programmable logic controller controlling each of the pumps. Upon receipt of a fault signal, the programmable logic controller activates the second, back-up pump to assure a full fluid dose is dispensed, and the dispensing process continues without interruption.
According to still another aspect of the invention, a method is provided for dispensing doses of a fluid comprising the steps of:
providing first and second pumps for pumping the fluid;
pumping the fluid from the source using the first pump;
sensing the flow of the fluid pumped from the first pump; issuing a fault signal when the first pump malfunctions; and,
activating the second pump to pump fluid from the source in response to the issuance of the fault signal.
According to yet another aspect of the invention a method is provided for dispensing doses of a fluid, comprising the steps of:
pumping doses of a fluid from a source of the fluid using a first pump;
sensing when the first pump malfunctions; and,
activating a second pump when a malfunction is sensed, in order to pump doses of the fluid using the second pump.
Accordingly, it is a primary object of the present invention to provide apparatus for dispensing doses of a fluid providing high reliability of operation, and continuous, uninterrupted dispensing of the fluid in the event of a pump malfunction.
A further object of the invention is to provide apparatus as mentioned above which provides automatic switch-over from a primary pump, to a back-up pump in an automatic manner, without operator intervention, so as to eliminate down time, and the possibility of operator error in correcting a malfunction.
A further object of the invention is to provide apparatus as mentioned above in which the switch-over to the back up pump is carried out automatically using a programmable logic controller which tracks the amount of fluid dispensed and maintains proper dosage levels, despite a pump malfunction.
A still further object of the present invention is to provide apparatus as described above which includes means for automatically sensing when one of the pumps has malfunctioned.
Another object of the present invention is to provide a method for dispensing doses of a fluid which provides automatic switch-over from a primary fluid pump to a back-up fluid pump in an automatic manner, while maintaining constant, repeatable quantities of fluids dispensed in each dose.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the present invention.